1. Field of the Invention
The present invention relates to a hypodermic syringe which is used for administering liquids such as medicaments to humans and other animals. Specifically, the inventive syringe here disclosed and claimed incorporates features which enable it to be filled and used conventionally and then rendered unfit for further use.
Recently the spread of diseases, especially the deadly disease known as AIDS, through the sharing of contaminated hypodermic syringes has received widespread public attention. It is now well known, for example, that hypodermic syringes used for administering illegal drugs frequently are used repetitively and by different persons with the consequent transmission of disease after the syringe needle becomes contaminated. A syringe that would not lend itself to repeated use would thus be helpful in combatting the spread of disease as well as the use of illegal drugs.
2. Description of Prior Art
Some hypodermic syringes, such as those which are prefilled with medicament, employ a coupling between the piston and the plunger rod which will break when a pulling force is applied to the plunger rod. Such syringes cannot be refilled and are thus unfit for repeated use. However, an attendant disadvantage of syringes with a break away piston/plunger rod coupling is that they cannot be filled by the user from a sealed vial, and many liquid medicaments are available only in sealed vials.
Hypodermic syringes which can be filled and used conventionally and then rendered unfit for further use are disclosed in U.S. Pat. No. 4,731,068 issued to John E. Hesse. These syringes, however, are quite complex, with attendant high production costs and increased likelihood of a malfunction which would allow the syringe to be reused.